He is more a general. less of a political leader, I don't think Malak would handle the politics very well. There are different types of sith. Some are more suited in warfare than others.

Sion is more subterfuge and convert warfare than Malak. Malak is great at overt warfare. Under the leadership of the Kotor 2 Sith Lords, they used convert warfare due to their much smaller fighting force. They can't do sustain warfare like Malak did.

The only reason that Republic won the Jedi Civil War is due to Revan leading a small convert strike team into the star forge and killing Malak. Malak was beating the crap out of the Republic by forcing them to over reach themselves.

Malak has never been redeemed and died as a Dark Lord. He admitted that he fail and wonder if he could be redeemed but knew that his time was over anyways.